Attorney General Cites 'Global Crisis' of Foreign 'Violent Extremists' in Syria's Civil War

WASHINGTON—Attorney General Eric Holder urged U.S. allies to toughen their strategy against the risk of Westerners traveling to fight in Syria's civil war and returning home radicalized and ready to commit domestic terrorist attacks.

That prospect amounts to "a global crisis," Mr. Holder said in Oslo on Tuesday, the first day of a five-day European trip to discuss the issue and others with justice ministers from allied...